The present disclosure relates to a grounding assembly for electronic equipment and a method for testing the resistance to ground of a grounding device in such assemblies. In particular, the disclosure relates to a grounding device and a grounding assembly having such a grounding device for use with outdoor electrical equipment that is subject to being damaged by lightning and a method for testing the resistance to ground of such a grounding device. An example of such electrical equipment is the electronic control systems used on underground irrigation systems, such as those installed on golf courses and the like.
Irrigation systems include numerous sprinkler heads and controllers located throughout a property. The controllers typically include a solenoid valve and one or more circuit boards which are typically connected to a central control computer and a power source by wires buried under ground. Lightning striking the ground far from a particular controller can induce voltage spikes in the wires leading to the controller that can destroy its circuit boards. Lightning arrestors are typically incorporated in such equipment to prevent this but for such arrestors to protect the equipment adequately they must have an effective connection to ground. Typically outdoor electrical systems, and especially irrigation systems with electronic controllers, include grounding assemblies which have multiple grounding devices. For further protection of electrically connected outdoor equipment such as irrigation systems the grounding assemblies of the controllers are connected or bonded to each other for added protection.
U.S. Pat. No. 8,081,415, the disclosure of which is incorporated herein by reference in its entirety, discloses various effective grounding assemblies which can be used in accordance applicable electrical codes. The grounding assemblies disclosed therein typically include two grounding devices for each of the controllers. These grounding devices can include a grounding rod and a grounding plate. When the grounding plate is buried in the soil it is surrounded by a suitable amount of a grounding enhancement backfill material, such as the backfill products sold under the trademarks PowerSet or PowerFill by Loresco International of Hattiesburg, MS. The backfill material enhances the conductivity between the ground plate and the surrounding soil.
The irrigation controller is typically enclosed in an above-ground housing which rests on a concrete pad. A conduit extends from the housing through the pad to an underground location. Underground wires extend through the conduit to electrically connect the controller to a power source and a central control computer. The controller includes a lighting protection board which is electrically connected to the grounding assembly. The grounding assembly can include a bus bar, a bridging wire electrically connecting the bus bar to the lighting protection board, a first grounding wire electrically connecting the bus bar to a first grounding device (e.g., a grounding plate) buried in the soil, a second grounding wire electrically connecting the bus bar to a second grounding device (e.g., a grounding rod) buried in the soil, and first and second bonding wires each electrically connecting the bus bar to either the ground of adjacent controllers or to a power supply ground. Bare copper wires have been used for the grounding and bonding wires, since they are connecting grounding devices or grounding assemblies of adjacent controllers. The grounding and bonding wires extend through the conduit from a location adjacent the bus bar to below ground level where the grounding and bonding wires emerge and separate towards their individual destinations.
In certain installations the grounding wires can be exposed to harsh soil environments that can result in premature corrosion of the grounding wires. In particular, it has been found that the interface between the grounding enhancement backfill material and the surrounding native soil is a harsh environment from a corrosion standpoint. Where the bare grounding wire emerges from the grounding enhancement backfill material and enters the surrounding native soil the bare grounding wire is particularly susceptible to corrosion. This can reduce the effectiveness of the ground.
In addition, when traditional bare grounding and bonding wires are routed through a conduit, testing of the resistance to ground of any individual wire can be frustrated as contact between the wires may occur within the conduit which can alter the circuit intended to be tested. Contact between the bare grounding and bonding wires and/or the conduit can result in false or ineffective testing of the resistance to ground measurement.